Tank to Wheel GHG rates are better for the gasoline engines by about the same percentage that WTW is better for the diesels, so it's about a wash.

As far as "which fuel pollutes more." diesel exhaust has at LEAST three known carcinogens and at least 40 harmful-to-human chemicals, while gasoline exhaust has many but fewer of the severely damaging chemicals.

From the California OHHEA website:

"Gasoline exhaust also contains cancer-causing 1,3-butadiene, formaldehyde and acetaldehyde. Diesel exhaust contains several dozen toxic substances and scientific studies have shown that workers exposed to diesel exhaust are more likely to develop lung cancer. Long-term exposure to particles in diesel exhaust poses the highest cancer risk of any toxic air contaminant evaluated by OEHHA. ARB estimates that about 70 percent of the cancer risk that the average Californian faces from breathing toxic air pollutants stems from diesel exhaust particles. The microscopic particles making up diesel exhaust particulate matter are less than one-fifth the thickness of a human hair. They are small enough to penetrate deep into the lungs, where they can contribute to respiratory disease."

So my guess is that the more diesel engines we keep off the road, the lower the lung cancer rates will be.